U.S. patent number 3,922,065 [Application Number 05/117,035] was granted by the patent office on 1975-11-25 for cube-corner retro-reflective article.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Thomas E. Schultz.
United States Patent |
3,922,065 |
Schultz |
November 25, 1975 |
Cube-corner retro-reflective article
Abstract
A retro-reflective monolithic article formed of transparent
material and having the array of cube-corner retro-reflective units
on the rear face divided into cells. The walls defining the cells
are formed integrally and extend directionally along the shortest
path formed by dihedral edges between adjacent apexes of the
retro-reflective units bordering each cell.
Inventors: |
Schultz; Thomas E. (Village of
Roseville, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
26814851 |
Appl.
No.: |
05/117,035 |
Filed: |
February 19, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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749239 |
May 31, 1968 |
|
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593948 |
Nov 14, 1966 |
3417959 |
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Current U.S.
Class: |
359/514;
359/530 |
Current CPC
Class: |
G02B
5/124 (20130101) |
Current International
Class: |
G02B
5/12 (20060101); G02B 5/124 (20060101); G02B
005/12 () |
Field of
Search: |
;350/97-109,67
;94/1.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Rubin; David H.
Attorney, Agent or Firm: Alexander, Sell, Steldt &
DeLaHunt
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a continuation of application Ser. No. 749,239,
filed May 31, 1968, now abandoned, which is a divisional
application of Ser. No. 593,948, filed Nov. 14, 1966, now U.S. Pat.
No. 3,417,959.
Claims
Having thus described the invention, what is claimed is:
1. A retro-reflective monolithic article formed of transparent
material and having a front and rear surface, the front surface
being smooth and the rear surface having a continuous array of
cube-corner retro-reflective units, said array being divided by
intersecting septa into a plurality of separate cells, each said
cell containing a plurality of said units, and said septa having
rear edges forming a continuous securable rear edge, characterized
in that said array is formed as a surface of continuous contiguous
rearwardly projecting cube-corner units each having a rearwardly
positioned apex formed by three rectangular mutually perpendicular
rearwardly converging facets forming three rearwardly converging
dihedral edges, and said septa are formed as continuous
intersecting walls extending rearward from a portion of at least
one of said facets forming said dihedral edges, having a width less
than a dimension of said facet, and directionally along the
shortest path defined by said dihedral edges connecting apexes of
adjacent units whereby said septa minimize the loss in
retro-reflectivity afforded by said facets from which said septa
extend.
2. A retro-reflective article according to claim 1 wherein said
front surface is planar and the rear edges of said septa project
rearward at least as far as said apexes.
3. A retro-reflective article according to claim 1 wherein said
septa have side walls extending generally parallel with the plane
of a facet of each of the projecting cube-corner units and extend
generally along straight lines dividing said article into
lozenge-shaped cells.
4. A retro-reflective article according to claim 1 wherein said
septa follow a zig-zag path and have side walls which are generally
perpendicular to a plane defined by the rear edges of said
septa.
5. A retro-reflective article according to claim 2 wherein said
article has a uniform thickness between said front surface and the
rear edges of said septa.
6. A monolithic retro-reflector structure for reflecting light back
toward the source thereof, said structure comprising a body of
transparent material having a substantially smooth light receiving
front surface area and a rear surface area immediately opposite and
coextensive with said front surface area, said rear surface area
having an array of contiguous cube-corner retro-reflective units
having rearwardly positioned apexes each formed by three
rectangular mutually perpendicular rearwardly converging facets
forming three converging dihedral edges, said array of cube-corner
retro-reflective units being continuous and divided by intersecting
septa, said intersecting septa defining a substantially continuous
rear support surface and dividing said rear surface area into a
plurality of separate isolated cells each containing a plurality of
said retro-reflective units oriented in the cells to reflect light
falling upon said front surface area, said units reflecting from
said structure light falling upon said front surface area in the
portion thereof corresponding to said cells and reflecting the
light back toward the source thereof to render said structure
highly visible at night, and said septa extending rearwardly from a
portion of at least one of the facets defining the converging
dihedral edges of said cube-corner retro-reflective units and along
the dihedral edges of adjacent units forming the shortest path
between the apexes of said adjacent units along the edges of said
cells.
7. A retro-reflective sheet material comprising
a monolithic article formed of transparent material having a smooth
light-receiving front surface and a rear surface opposite said
front surface and coextensive with said front surface, said rear
surface having a continuous array of cube-corner retro-reflective
units having apexes each formed by three rectangular mutually
perpendicular rearwardly converging facets forming three converging
dihedral edges and having intersecting septa, said septa extending
rearwardly from a portion of at least one facet forming said
dihedral edges adjacent said edge, and directionally along said
dihedral edges joining the apexes of adjacent units for dividing
said rear surface into a plurality of separate cells each
containing a plurality of said units, said septa having rear edges
positioned rearwardly a distance at least equal to that of the
apexes of said units, and
a backing joined to said rear edges of said septa to define
hermetically sealed cells in said material.
Description
This invention relates to a retro-reflective article and to a die
for forming the same.
In one aspect this invention relates to an improvement in
retro-reflective plate-like articles having cube-corner
retro-reflective units embossed on one surface thereof with the
articles divided into cellular sections by septa embossed on the
same surface as and separating numbers of said units. The septa are
formed to connect adjacent apexes of the units and extend
directionally along the dihedral edges forming the shortest path
between said apexes. The free edges of the septa are available for
bonding a backing sheet to the articles to form retro-reflective
sheet material having a long useful life. The articles and backing
sheet in combination define a plurality of separate hermetically
sealed cells.
The retro-reflecting article of the present invention affords
increased brilliance for a cellular cube-corner retro-reflective
sheet by having the septa defining the cells in the article extend
directionally along edges of the facets forming the cube-corner
units. This structure has an advantage in that only the
retro-reflectivity of the very corner or apex and the reflectivity
of two or three dihedral edge portions of the cube-corner, from
which extend a septum, are destroyed and not the retro-reflectivity
of the entire cube-corner since portions of the side walls of said
units are still present which define the greatest reflective area
of the unit. The amount of retro-reflection actually lost is a
fraction of a cube-corner unit, not an entire unit as is the case
if the septa are formed at random across the face of a plate
embossed to form cube-corner units on a surface.
The above and further objects and advantages of the present
invention will be more readily apparent after reading the following
description which refers to the accompanying drawing wherein:
FIG. 1 is an enlarged fragmentary view of a face of a die member
formed to provide an article in accordance with the present
invention from one type of member;
FIG. 2 and FIG. 3 are respectively a side view and an end view of
one type of pin used in the die of FIG. 1;
FIGS. 4 and 5 are respectively a side view and an end view of a
second type of pin;
FIGS. 6 and 7 are respectively a side view and an end view of a
third type of pin;
FIGS. 8 and 9 are respectively a side view and an end view of a
fourth type of pin used in the die of FIG. 1;
FIG. 10 is a fragmentary sectional view of a mold showing the die
of FIG. 1 in the movable member and in cross-section;
FIG. 11 is an enlarged fragmentary rear view of the product formed
by the die of FIGS. 1 and 10;
FIG. 12 is an enlarged fragmentary vertical section showing the
final retro-reflective sheet product;
FIG. 13 is an enlarged fragmentary view of a second embodiment
showing a face of a die formed from another embodiment of the
members;
FIG. 14 is a perspective view of one type of pin used in forming
the die of FIG. 13;
FIG. 15 is a perspective view of a second type of pin used in the
die of FIG. 13;
FIG. 16 is a perspective view of a third type of pin used in
forming the die of FIG. 13;
FIG. 17 is a perspective view of a fourth type of pin used in
forming the die of FIG. 13;
FIG. 18 is an enlarged fragmentary sectional view of a press
showing a die constructed in accordance with FIG. 13;
FIG. 19 is an enlarged fragmentary rear view of the product formed
by the mold of FIG. 18;
FIG. 20 is an enlarged fragmentary vertical section showing the
final retro-reflective sheet material formed in accordance with the
present invention from the die of FIGS. 13 and 18; and
FIG. 21 is a fragmentary perspective view of another embodiment of
the members for forming a die to mold articles in accordance with
the present invention.
Referring now to FIG. 1 of the drawing, a portion of the face of a
die, generally designated by the reference numeral 30, is
illustrated. This die 30 is formed of members nested together to
form an array of cube-corner trihedrons. These trihedrons do not
correspond to the portion of a cube divided by a diagonal plane,
but consist of three full adjacent sides of a cube. The array is
produced by nesting together a plurality of members formed at one
end with three generally square plane surfaces or facets joined at
right angles. The members in this group are pins which have a
regular hexagon cross-section. FIGS. 2 and 3 show a typical pin 32
for forming this die, which pin or hexagonal bar is made of a
convenient length and at one end is pointed by cutting three plane
square surfaces 33, 34 and 35 which are perpendicular to each
other, and when the pins are grouped parallelly with a different
surface on each of three pins disposed in mating engagement, form a
depression which is also a cube corner. Additional elements placed
in a similar assembled relationship therewith produce an array of
cube-corner depressions which upon molding produce cube-corner
retro-reflective units. The die forms an article which has not only
the retro-reflective units but also wall members or septa which
divide the units into sections or cells. The septa are formed in a
manner to minimize the loss in retro-reflectivity and to afford
free end surfaces for bonding a backing sheet to the article.
In FIG. 1 a plurality of the pins 32 are grouped to form
cube-corner depressions, and these pins are grouped with three
other preformed types of pins to form a die for molding an article
in accordance with the present invention.
FIGS. 4 and 5 illustrate the second pin used in forming the die for
molding an article of the present invention. This pin 37 has a
cross-section which is a regular hexagon and is made of a
convenient length with three plane surfaces 38, 39 and 40 formed at
one end thereof, which surfaces are perpendicular to each other,
forming a trihedron on the end of the pin. Pin 37 however has a
portion of one side wall cut away adjacent the end of the pin to
form a notch 41. The notch 41 extends parallel along one side wall
of the pin 37 and thus along one edge of the facet 39, reducing its
area so it would no longer be a square, and the wall 42 of the
notch would also truncate a corner of the facet 38, as shown in
FIG. 4. The wall 42 is generally parallel with the side wall of the
pin, but sufficient draft is permitted for release of an article
formed thereby from a mold. The bottom 43 of the notch 41 is
perpendicular to the side wall of the pin. The pins 37 are
positioned adjacent corners of each of the sections of the die 30,
forming a cell. This will be described in greater detail
hereinafter.
FIGS. 6 and 7 show a third pin wherein the pin 44 is again a
regular hexagon of a convenient length and pointed at one end by
three perpendicular surfaces 45, 46, and 47. This pin differs from
the pins 32 and 37 however in that it has a recess or notch formed
in two adjacent side walls of the pin which extend directionally
along the edges of facets 46 and 47. The walls 48 and 49 of the
notch are generally parallel with the side walls of the pin,
allowing for suitable draft, and join with each other. The pins 44
are positioned in the die matrix to define the sides of the
sections.
The fourth type of pin used in the matrix of FIG. 1 is illustrated
in FIGS. 8 and 9. This pin 51 is also hexagonal, made of a
convenient length, and pointed at one end by three plane
perpendicular surfaces or facets 52, 53, and 54. The end of this
pin 51 however is formed with a notch in four consecutive sides of
the pin which extend directionally parallel to edges of all three
facets. As shown, it extends along one edge of the facets 52 and 54
and along two edges of facet 53. The walls of the notch form
triangularly shaped wall surfaces as shown in FIG. 8 which are
generally parallel to the side wall of the pin, except for the
allowance of suitable draft. The pins 51 are used in conjunction
with pins 37 to define the adjacent corners of four sections of the
die.
Referring again to FIG. 1 it is shown that a number of each of the
four types of hexagonal pins are assembled in a manner such that
the notches in the pins 37, 44, and 51 are interconnected to form
continuous slots across the face of the die, dividing the die into
sections with each section having sufficient uninterrupted facets
to define between 2 and 12 perfect cube corners, i.e., each cube
corner having three complete adjacent sides of a cube.
FIG. 10 illustrates schematically a mold for forming an article
having a generally plate-like appearance with a plurality of
cube-corner retro-reflecting units and septa on the rear surface
thereof. The mold may include a fixed portion 61 having a cavity
with an interior planar surface 62 for forming the front side of an
article. The surface 62 is joined by generally perpendicular walls
63. An opening 64 is formed in one of the walls 63 and communicates
with a conduit 65 through which material may be injected into the
mold to form the article.
The movable portion 66 of the mold is adapted to receive the die
30, and mates with the fixed portion 61 to define a spacing between
the apexes of the various pins 32, 37, 44, and 51 and the surface
62, defining the article thickness. Conventional injection molding
techniques may be used to form the article having the
retro-reflecting units, or the same could be formed by pressing.
Suitable release pins (not shown) may be positioned in the die 30
to eject the article from the mold. These release pins could extend
through an edge of a pin and communicate with a recess.
FIG. 10 also illustrates the cross-section of the die and
illustrates that the notches extend slightly below the lowermost
corners in the face of the die.
FIG. 11 is a view of an article, generally designated 70, formed by
the die 30. This article is formed of transparent material and is
plate-like having a uniform thickness with a smooth planar front
side and a rear side, which is shown in FIG. 11, formed with
retro-reflective units, the apexes of several being designated by
the numeral 71. On the rear side are also formed walls or septa 73
which extend continuously along undulating paths around several
units 71, and divide the rear surface into cells which preferably
contain not less than two nor more than 12 units, and as
illustrated, contain four. It will be noted in FIG. 12 that the
finished retro-reflective sheet material comprises the plate 70 and
a backing sheet 75 bonded together between the free edges of the
septa 73 and the surface of the backing sheet 75, and divide the
void between the plate 70 and sheet 75 into definite cells, whereby
the four uninterrupted totally reflex-reflective cube corners are
enclosed within a single cell. The septa 73 extend perpendicularly
from the rear surface of the plate and directionally along the
dihedral edges of a unit 71 to connect, along the shortest path,
the apexes of adjacent units to define the boundary of each cell.
The septa 73 extend rearward at least as far as the apexes and
terminate in smooth continuous interconnecting free edges which
have a width sufficient to afford an adequate sealing surface to
which is bonded the sheet 75. In use, light directed toward the
surface 72 would be refracted and reflected within the plate 70 to
emerge from the plate 70 back toward the source of the light.
Referring now to FIGS. 13 through 18, the second embodiment will be
described. FIG. 13 shows a fragmentary view of the face of a die
80, for forming an article according to the present invention,
formed by pins having a square cross-section with the ends
staggered a distance equal to the thickness of the pins and with
the longitudinal axis of the pins disposed on a slant. The face
formed by the adjacent sides and end of each pin define a plurality
of square planar facets affording an array of cube-corner
projections and depressions and a plurality of intersecting slots
or grooves which extend across the die face dividing it into
lozenge-shaped sections or cells.
The grooves in the die are formed by the nesting of preformed pins
to define a given pattern. The pins forming this die are
illustrated in FIGS. 14 through 17. FIG. 14 illustrates the typical
pin 81 which is square in cross-section with an accurately cut and
surfaced square end 82, perpendicular to the longitudinal axis of
the pin. Three pins of this construction disposed in a parallel
staggered relationship will define a cube-corner depression
suitable for forming upon molding a cube-corner retro-reflecting
unit.
The second type of pin 84, illustrated in FIG. 15, is also square
in cross-section and is formed with an accurately cut end 85 which
is perpendicular to the longitudinal axis of the pin. Adjacent the
end 85 and formed generally parallel with respect to two sides of
the pin 84 are notches 86 and 87. These notches 86 and 87 extend
from a point slightly below a common corner of the pin 84 and
surface 85 downwardly along the sides of the pin at an angle of
45.degree. relative to surface 85. The shoulder formed on the side
of the pin, defining the bottom of the notches 86 and 87, are not
perpendicular with the sides of the pin but are disposed at an
angle such that in the assembled position the groove formed in the
face of the die by such notches will have a bottom disposed in a
plane parallel with that of the apexes of the trihedrons formed by
the adjacent sides and end of the pins. This pin is used to form
the corners for the sections on the die.
The third pin 90 used in the die of FIG. 13 is shown in FIG. 16.
Pin 90 is also square in cross-section and has an end which is
perpendicular to the longitudinal axis of the pin. The pin 90 has a
notch 92 formed in one side (along the left edge) of the pin which
corresponds generally to the notch 87 in pin 84. The notch 87 is
disposed at an incline relative to the surface 91 to form,
respectively, slots along the top and bottom edges of the cells on
the die 80 as viewed in FIG. 13.
The fourth type of pin used in the die 80 is shown in FIG. 17 and
is identified by the numeral 95. Pin 95 is square in cross-section
and has an end surface 96 perpendicular to the longitudinal axis of
the pin and a notch 97 is formed in one side wall (along the
forward edge) of the pin adjacent the surface 96 and extending
along said side wall at an angle inclined relative to the plane of
the end 96 in a manner corresponding to notch 86 on pin 84. This
incline is from the left side downwardly from surface 96 to the
right side wall. The pin 95 is used to define the right and left
edges of a section on the die, thus forming septa on the sides of a
cell. The walls defining a side of the notches 86, 87, 92 and 97
are generally parallel to the side walls of the pins but are formed
with sufficient draft to permit release of the cube corner article
from the face of the die 80.
FIG. 18 shows a single cavity mold having a fixed portion 100 which
is formed with a cavity having a flat planar surface 101 connected
by perpendicular side walls 102. An injection conduit 103 is
disposed in one of the side walls 102, permitting the injection of
material into the mold. The movable portion 104 of the mold is
formed with a cavity, in which is placed in a predetermined array,
a number of pins 81, 84, 90, 95, to define a pattern forming a die
80 having a cube-corner forming face as illustrated in FIG. 13. The
pins are disposed on a slant such that the end surfaces and
portions of adjacent sides define the cube-corner projections and
depressions. The pins positioned as illustrated define several
depressions each of which has three complete cube walls. By
injecting material into the mold of FIG. 18 in the conventional
manner and allowing the same to set, an article 105 (FIG. 19) is
formed which has a smooth planar front surface and a rear surface
formed with cube-corner retro-reflecting units 106 and septa 111
and 112. The septa 111 and 112 extend directionally along the
dihedral edges of facets forming certain of the units 106 and
connect adjacent apexes of said units.
Suitable release pins (not shown) must be positioned in the die to
eject the molded article from the face of the pins. These release
pins may be positioned to engage the septa formed on the rear face
of the article 105 and may extend through certain of said pins
parallel to the axis thereof.
A rear side view of the article 105 formed by the die of FIG. 13 is
illustrated in FIG. 19. The article 105 may have bordering septa
111 corresponding to the angle and direction of dividing septa 112,
and the septa 112 are formed with free securable edges having a
width sufficient to afford easy bonding thereto of a backing such
as the sheet 113, illustrated in FIG. 20. It will be noted that the
septa should project from the rear face of the article at least to
the imaginary surface generated by the apexes of the cube-corner
units 106, and as illustrated in the sectional view (FIG. 20) the
septa extend beyond the apexes of the cube-corner retro-reflective
units 106. A backing sheet 113 can thus be bonded to the surfaces
of the septa to hermetically seal the units 106 in a cell.
A third embodiment of the members for forming a die in accordance
with the present invention is illustrated in FIG. 21. This figure
of the drawing illustrates a die 120 formed of plate-like elements
121 with one saw-tooth-type edge formed by square surfaces having
equal 90.degree. dihedral angles, with the dihedral edges extending
transversely of the plates and normal to the sides of the plates.
Plates 121 are located to position the surfaces congruously to form
trihedral depressions, with the dihedral upper edge of a ridge or
tooth 122 aligned with and disposed in the same plane as a groove
line on the dihedral edge formed between two teeth. The die face
formed will correspond generally to that shown in FIG. 13. Notches
123 may be routed transversely through the plates along edges of
the square facets and obliquely to the plane of the plates to form
the septa in the molded article. Additionally, material may be
removed from sides of the plates adjacent the saw-toothed edge to
form recesses 124 running generally parallelly with the edges of
the plates, allowing again for draft, as illustrated at 124.
It is desired that the cells in the articles such as 70 and 105 be
as small in size as possible but yet the reflectivity of an article
must, as a practical matter, be sufficient such that the
non-retro-reflective area caused by the septa interferring with the
retro-reflectivity of certain units do not constitute an area
greater than that defined by retro-reflecting units. Preferably
retro-reflectivity of the article results in a measure of at least
400 candle power per foot candle per square foot measured at
0.2.degree. divergence from a beam at -4.degree. incidence to the
front face. The cells should be as small as possible and therefore
preferably have a retro-reflective area not less than 0.06 square
inch (4 square millimeter) or greater than one square inch (6
square centimeters) and should include not less than 2
retro-reflecting units. The septa have a free edge which is at
least 1/100 inch (0.2 mm) and preferably not over 1/8 inch (3 mm),
and indeed not over 1/4 inch (6 mm).
The backing as illustrated in FIGS. 12 and 20 is preferably a
material which is essentially vapor impermeable and durable when
exposed to the weather. Examples of such materials for the backing
are aluminum sheeting, galvanized steel, various laminates and/or
durable polymeric film-like sheet materials suitably formed, for
example of polymethyl methacrylate, polyestes, polyamides,
polyvinyl fluoride or polyvinyl chloride. This backing may be
flexible or rigid, but it must be bonded to the free edges of the
septa providing a multiplicity of hermetically sealed cells which
are each free from contamination by dust particles or moisture to
maintain a substantially continuous prism-air interface on the
smooth facets of the retro-reflecting units. There is no silvering
or other reflective coating on the units. In fact, such coatings
only degrade or diminish the retro-reflectivity of the article.
The free edges of the septa may be bonded to the backing by various
means such as heat sealing (using a grid next to the backing
corresponding to the pattern of the septa); adhesives, either
pressure sensitive or heat or solvent activatable adhesives; or by
using a solvent which attacks the septa to make the free edge tacky
and, preferably, the backing material to thus form a bond. The
adhesive may be applied to the face of the backing, to the face
edges of the septa or to both. Further, a polymerizable syrup, e.g.
methylmethacrylate syrup, could be applied to the backing or septa
to bond the articles. It is important, however, to avoid exposure
of the facets forming the retro-reflecting units to the solvents,
adhesives or excessive heat.
* * * * *